I. Field of the Invention
This invention relates to a process for forming the tubular members of a vehicle manifold and, in particular, to forming the compound curvatures of the tubular member using cooperating die sets and a hydroforming process to maintain an internal fluid pressure preventing deformation of the tube during bending.
II. Description of the Prior Art
Various metal forming processes are known for creating complex configurations from a metal blank. Sheet metal may be stamped and stretched to form the desired configuration. Tubular blanks have been bent, stretched and radially expanded to form complex configurations. However, depending upon the size of the tubing and the complexity of the desired configuration, crimping or buckling may occur at the inner radius of the bend. In past situations, the inner radius has been supported to guide the compression at the inner surface as the outer surface is stretched. Nevertheless, even with support certain configurations simply cannot be formed without deformation of the tubular member.
Hydroforming of metal components was developed to alleviate the deformation of the metal during bending, stretching, etc. into complex configurations. The general principal of hydroforming comprises applying a predetermined fluid pressure to an area of the metal to be manipulated. In the case of a tubular member, an internal fluid pressure is applied as the tube is bent and stretched. Typically, this is accomplished by immersing the tube in a fluid bath to fill the tube, applying end plugs to the tube which are used to increase the internal pressure to a predetermined level and bending the tube along a plane perpendicular to the die stroke. Under certain procedures, the tube may be bent around a die to the desired configuration. The hydroforming process may also be used to radially expand sections of the tube by increasing the internal pressure at that region.
Despite the advantages a hydroforming process provides in manipulating metal without deformation, the complexity of the bent tube is limited by the dies used in the process. The known hydroforming processes bend the tube only in a single plane. Modern components are becoming increasingly complicated requiring compound bends. The hydroforming process lends itself to the formation of complex tubular products without deformation of the metal material.